1. Field
Disclosed herein is a laminated core with soft-magnetic material and a method for joining core laminations by adhesive force to form a soft-magnetic laminated core. The laminated core comprises core laminations which form a core lamination stack. Between the core laminations, the core lamination stack is provided with intermediate layers. These intermediate layers allow the stacked core laminations to be joined by adhesive force to form a laminated core with soft-magnetic material.
2. Description of Related Art
From DE 27 20 531, there is known a method for bonding coated parts, in particular laminated cores of electric motors, by means of an epoxy adhesive, wherein the coated parts are brought into the desired position and then impregnated with the resin using a capillary action, wherein the epoxy adhesive is mixed before the impregnation process with a carrier containing a solvent which reduces the viscosity of the adhesive to a level required for the capillary action. DE 27 20 531 therefore describes the chemistry of the capillary adhesive and solves the problem of changing a viscous, honey-like adhesive in such a way that it becomes thin-bodied and can be used as a capillary adhesive; this is achieved by adding a solvent or a suspension liquid to the adhesive.
As a result of this property, the adhesive shrinks enormously in the drying and curing process, causing strains and negative effects on the magnetic quality of the soft-magnetic laminations. As a result of an associated process-related significant pressure follow-up of the laminated cores, a further degradation of the magnetic quality has to be expected. This has particularly negative effects in a magnetically highly-saturating CoFe laminated core, which invariably has a high magnetostriction, leading to losses in the soft-magnetic properties of the laminated core.
Other conventional methods are known from DE 24 46 693 B2, which relates to the production of electromagnetic components, in particular chokes. To form a stack of bonding laminations, an impregnating resin is used, which results in the problems described below. DE 1 613 312 further discloses a method for bonding magnetic sheets wherein a lacquer is applied to the sheets, which likewise which results in the problems described below.
In these conventional methods for joining core laminations by adhesive force, an adhesive is applied by brushing, spraying or dipping the individual laminations into the adhesive. In these methods, the adhesive consists of solvent-based, diluted adhesive systems. After the solvent has been dried off, the dry, coated laminations are joined to form stacks, whereupon the adhesive is cured. These known methods involve the problem that only relatively thick and uneven adhesive layers can be applied. In capillary processes, known solvent-containing adhesive systems are used, which have the disadvantages described above with respect to magnetic degradation.
FIGS. 7 to 11, for example, illustrate the production of soft-magnetic laminated cores according to prior art. FIG. 7 is a diagrammatic cross-section of a soft-magnetic sheet 5 made of a soft-magnetic material 3 and having a top side 9 and an underside 10. As FIG. 8 shows, the top side 9 and the underside 10 are provided with a coating 13 intended to insulate the core laminations to be stacked from one another electrically. For this purpose, a final annealing of the soft-magnetic sheet 5 may for example be carried out in an inert atmosphere, followed by oxidation annealing in air or a water vapour atmosphere, in order to adjust the soft-magnetic properties of the material on the one hand and to obtain an electrically insulating coating on the other hand. In this final annealing process, a volume increase caused by recrystallisation processes of rolled soft-magnetic sheets is to be observed, this revealing itself in a change in the length and width of the sheet section.
In FIG. 9, the coated soft-magnetic sheets 5 of FIGS. 7 and 8 have been separated in a forming step to form core laminations 4, the contour surfaces 11 now exposing the soft-magnetic material 3. A second annealing process can now be performed, which does however not involve any further volume increase or growth in the length and width of the core laminations 4.
As FIG. 10 shows, an adhesive 8 is then applied to one side or both sides 9 and 10 of the core laminations, and several core laminations 4 coated with the adhesive 8 are then pressed together in the direction of arrow A as shown in FIG. 11. As many core laminations 4 with relatively uneven adhesive layers 8 in between are pressed together to form intermediate layers 7, various regions of the core laminations 4 are warped by warping 16 as shown in FIG. 11, so that stresses are introduced into the soft-magnetic material to the detriment of its soft-magnetic properties.
In addition, the adhesive emerging at the sides of the core laminations 4 in the pressing process has to be removed from the end faces and contour surfaces of the laminated core 2 in complex reworking steps. One disadvantage of such laminated cores 2 from prior art lies in the insufficient parallelism of the bonded core laminations and in the need to rework the laminated core 2. In addition, the relatively thick and undefined adhesive joints which remain between the core laminations have the effect that the fill factor is relatively low and the positive soft-magnetic properties of crystalline CoFe alloys do not show to advantage.
As the core laminations to be joined have to be clamped, as the adhesive is softened and then cured, adhesive escapes in a disadvantageous and relatively undefined way at the circumference or the contour surface of the core. As a result, laminated cores are as a rule produced with insufficient plane parallelism and then have to be brought to scale by mechanical machining both in terms of thickness and as a result of the adhesive leakage at the contour surfaces. These reworking steps can result in short-circuit links between individual core laminations, which in turn lead to eddy current losses in the core. These eddy current losses adversely affect the magnetic properties of these cores.
A further disadvantage of laminated cores joined by adhesive force in this way lies in the fact that the adhesive layer is too thick relative to the thickness of the core laminations, so that the packing density of the core is low. This reduces the soft-magnetic mass relative to the core volume, so that the advantages of a soft-magnetic material, preferably a CoFe alloy, cannot be utilised to the full. In addition, such a laminated core has adhesive layers of varying thickness in the intermediate layers, so that the core laminations have a reduced parallelism from the topmost to the bottom lamination of the laminated core. The required mechanical reworking of the magnet material of the completed laminated core results in magnetic losses, which should be avoided if possible.